DIRECT OBSERVATION OF THE ELECTRON SPECTRAL-FUNCTION IN THE INTEGER AND FRACTIONAL QUANTUM HALL REGIMES BY RESONANT-TUNNELING

Low-temperature current-voltage characteristics of a double-barrier re sonant tunnel junction are used to directly measure the two-dimensiona l (2D) electron spectral function. Our data provide quantitative deter mination of the 2D density of states, including chemical potential and linewidth oscillations as a function of magnetic field up to 51 T. We also measure a chemical potential jump at 1/3 fractional filling of t he lowest Landau level.